1. Field of the Invention
The present invention relates to the field of digital in-circuit testing. More specifically, the invention relates to a method for creating an in-circuit test for a device.
2. Related Art
In-circuit test is a test wherein the performance of each digital integrated circuit (IC) on a board is independently tested as a functional unit. In order to perform in-circuit test, a tester must apply input signals directly to the inputs of a DUT (device under test or to be tested) and must access the outputs of the DUT to observe the output response. A "bed-of-nails" (i.e., probes that directly make contact with the device I/O pins from pads on the surface of the board) fixture is used to provide access to the required nodes on the board. Each digital IC on the circuit board can then be tested as if it were electrically isolated from the circuit. In-circuit testing is described in detail in U.S. Pat. No. 5,004,978, entitled "Method for Regenerating In-Circuit Test Sequences for Circuit Board Components," the full text of which is incorporated herein by reference.
One requirement for in-circuit test is that complete stimulus and response patterns be known to the tester for each device to be tested. The stimulus and response patterns for a device are known as a "test routine." Each test routine is stored in a device model in a device models library. As a result, tests for many common digital IC's can be programmed once, in advance, stored in the library, and then called upon when needed. This greatly simplifies test generation since this pre-programmed test can be used over and over again.
In many instances, test information for a device will not be known. As a result, no test routine is available. If no test routine is available in the library, a test engineer has conventionally been faced with two choices. First, he or she could generate a test for the device. This is the preferred choice because once the test has been generated, it can be added to the library for future use. However, with a new device, the information required to generate a test (e.g., a manufacturer's specification sheet) may not be available.
The second choice available to the test engineer is to skip testing the device. While this results in the device not being tested in the in-circuit configuration, it is often the only choice available to the test engineer.
What is needed is a method for creating an in-circuit test for devices about which little information is available.